US D575823 S1
The ornamental design for a writing instrument, as shown and described.
FIG. 1 is a side view of a writing instrument of the present application seen from the left side of the writing instrument as shown in FIG. 4;
FIG. 2 is a rear view thereof;
FIG. 3 is a side view seen from the right side thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a bottom view thereof shown on an enlarged scale; and,
FIG. 6 is a top view thereof shown on an enlarged scale.